1. Field of the Invention
The present invention relates to methods of manufacturing spindle motors, and the spindle motors manufactured through the methods.
2. Description of the Related Art
Spindle motors are mounted in hard disk drives for use in, e.g., personal computers and car navigation systems to rotate magnetic disks around central axes thereof. A spindle motor includes a stator unit that is fixed to the housing of a hard disk drive and a rotor unit that is rotated relative to the stator unit with a magnetic disk loaded thereon.
Among various types of spindle motors, a spindle motor of a stationary shaft type is provided with a shaft as part of the stator unit, and the rotor unit is rotated around the shaft. In such a spindle motor of a stationary shaft type, the rotor unit includes a sleeve that is inserted in a rotatable manner relative to the shaft and a hub that is rotated together with the sleeve. The hub is provided with a flange surface to mount a disk thereon.
For example, Japanese Unexamined Patent Publication Nos. 2000-354349, 2002-5171, and 2005-48890 disclose the structure of such a conventional spindle motor.
In the above-mentioned spindle motor, the inner peripheral surface of the sleeve and the flange surface of the hub are closely relevant to the attitude of the magnetic disk and the rotational accuracy. That is, the magnetic disk should be rotated stably in an attitude normal to the central axis of the shaft. For this reason, the inner peripheral surface of the sleeve and the flange surface of the hub are desirably finished with a high degree of accuracy such that the inner peripheral surface of the sleeve, which opposes the outer peripheral surface of the shaft, is parallel to the central axis, and that the flange surface to support the magnetic disk is normal to the central axis.
If the inner peripheral surface of the sleeve and the flange surface of the hub are imperfectly finished, the magnetic head floats unstably over the recording surface of the magnetic disk, which may be a setback for high-density recording.
In addition, a slight distortion inevitably occurs both in the sleeve and the hub in fixing them. Such a distortion in the sleeve and the hub may adversely affect the attitude of the disk and the rotational accuracy.